Acid / Base
Titration
Professor Bob
Kaplan University
Department of Science
The most distinctive feature of an acidic or
basic compound is ionic dissociation.

Compounds dissociate into their
individual cations and anions.
Acids  H+ cations
Bases  OH- anions
Strength of an acidic or basic compound is
determined by the degree of dissociation.
Less stable compound
 More ionic dissociation
 More charged ions in solution
 Stronger acid or base
HCL  H+ + ClStrong acid driven to products.
Products produced includes: H+ cations
More products ( more H+ )  Stronger acid
Strong acids dissociate completely
to form products.
pH indicates degree of dissociation.
pH measures the concentration of H+ ions.
ph  [ H+ ]
pOH  [ OH- ]
ph = - log [ H + ]
[ H + ] = 0.1 M = 10 -1 M
log 10 -1 = - 1
- log = 1
[ H + ] = 0.000001 M = 10 -6 M
log 10 -6 = - 6
- log = 6
Lower pH  Higher Acidity
Strong acids dissociate to products
HCL  H+ + ClMeasure strengths by Dissociation Constant
K =
Larger K  Higher [ H + ]
Smaller K  Lower [ H+ ]
Stronger acid  Higher [ H + ]
Larger K  Stronger acid
NaOH  Na+ + OH-
K =
Larger K  Higher [ OH - ]
Larger K  Stronger base
Sulfuric Acid
H2SO4 --> 2 H+ + SO4
2 protons liberated per molecule.
Phosphoric acid (in soda pop)
H3PO4 --> 3 H+ + PO4
3 protons liberated per molecule !
Acids produce H+ cations
HCl = H+ + ClEach mole of HCL produces 1 mole of H+
Bases produce OH- anions
NaOH = Na+ + OHEach mole of NaOH produces I mole OH-
H+ + OH- = H2O
pH 7 = neutral point
ph 7: [ H+ ] = [ OH- ] = 10 -7
Ionic concentrations are equal.

Investigate the strength of 5 different
commercial antacids by chemical titration.

A titration is a controlled way of measuring the
amount of acid it takes to neutralize the base.

If you know how much base is used,
then you can tell how much acid is present.

Using HCl and NaOH as our acid and base,
All mole ratios are 1:1.
In the chemistry laboratory, we use volumetric
measurement for solutions. Examples include:
Beakers, flasks, burettes, pipettes,
eye droppers
Typically in liters (L) or milliliters (mL)
Control the volume of acid or base using a stopcock
1-way valve at the base of a calibrated buret in order
to deliver the solution of acid or base drop-by-drop.
Measurement of the concentration of solution.
M = Molarity
Molar concentration = moles / liter = M
Measure volume in liters (or milliliters ml)
Vol ( L ) x Conc. ( mol / L )
= Number of Moles
Our objective is to determine how much base is in
each antacid tablet. To determine this indirectly:
 Neutralize the base with an acid.
Since we have a 1 : 1 ratio of acid : base
Number of moles of acid added
= Number of moles base in antacid tablet
Begin by adding extra acid.
Add 40 mL of 0.1 molar HCl to each one
How many moles of acid is that ?
( 40 mL ) * ( 1 liter / 1000 mL ) = 0.040 liters
Vol. x Conc. = Moles
( 0.040 liters ) ( 0.1 moles / liter ) = 0.004 moles
View this 0.004 moles HCl as stomach acid.
That is the total amount of stomach acid after
dinner tonight. Then eat one tablets
But one tablet is not enough.
•
So in order to neutralize all of the acid,
 Add MORE base.
The strongest tablet (base) will require
the least addition of more base.
The strongest tablet will
already have the most base
and will thus require the
least addition of more base (NaOH).
That is the key to the first question.
Thus, there are no calculations necessary.
It is purely qualitative.
Compare volumes of added NaOH
Not all tablets weigh the same amount.
Break it down to a "per gram" basis
Change the volume added to:
Moles per gram
Moles added / gram dosage
Maalox requires 24.1 mL NaOH
NaOH Concentration = [ NaOH ] = 0.05 M
Molarity = M = moles / liter
( 0.024 L ) x ( 0.05 moles / liter)
= 1.21 x 10 -3 Moles
Consider the weight of each tablet in grams
Maalox: 20.0 grams
Want moles / gram
Divide the number of moles by
the weight of that tablet in grams
[ 1.21 x 10 -3 moles ] / 20 grams
= 6.05 x 10 -5 mol / g
So which is the strongest antacid
tablet on a per gram basis ?
•
Which tablet requires the least
amount of acid to neutralize the base
in the tablet …..
…..in moles / gram ?
•
See the following websites:
http://en.wikipedia.org/wiki/Acidbase_titration
http://en.wikipedia.org/wiki/PH_indicator
H2SO4 is a diprotic acid.
It releases 2 protons (H+) per acid molecule.
H2SO4 = 2 H+ + SO4 (2-)
Thus, it is likely to be at least twice as strong.
Thus, at the same concentration (0.1 M),
we need to add only half as much acid.
Balance the equation:
Al (OH)3 + HCl  AlCl3 + H2O
*Hint:
There are 3 hydrogen atoms on the left,
and only 1 H atom on the right
 3 H2O needed on the right.